Structured lighting systems illuminate a scene with light from a source (such as a laser or light source having a characteristic wavelength) and utilize one or more imaging devices (such as a CCD camera, focal plane array, other pixilated imaging device) to observe the light from the illumination source that is reflected from objects and surfaces within the scene. The pixel location(s) in the imaging device(s) receiving reflected light can be correlated or mapped (e.g. by triangulation) to provide positional and shape based information about objects and surfaces within the scene.
Structured lighting systems are employed in applications including for example, mapping, autonomous navigation, dexterous manipulation, surveillance and reconnaissance, part inspection, geometric modeling, laser-based 3D volumetric imaging, simultaneous localization and mapping (i.e. “SLAM”), aiding first responders, and in support of soldiers with helmet-mounted laser imaging and detection and ranging (i.e. “LADAR”) systems. The use of structured lighting systems can involve processing images of a scene to segment (e.g. distinguish, resolve, and/or isolate) the reflected light from an illumination source, from the background illumination of the scene. For example, image processing can be used to segment the reflected light of a laser illumination source, from background sources of illumination that can include the natural lighting of a sunlit scene, or from secondary sources (natural and manmade) of light that may occur in the scene. The success of a structured lighting application can depend on the ability of the system to segment the reflected illumination of a source, from the background illumination.
Segmenting the reflected light of an illumination source in a scene, can be problematic when the energy received from background illumination, i.e. background clutter, is on the order of, or greater than, the reflected energy from the illumination source. Segmenting the reflected light of an illumination source is further complicated when the scene comprises surfaces that are highly absorptive of the light from the illumination source, for example, as can occur in the case of asphalt surfaces. Additional complications arise when the scene is dynamic, i.e. changing or moving. For example, a scene can be spatially dynamic as in the case where the imaging device is moving relative to objects within the scene. Also, the scene can be temporally dynamic, as can be the case when the intensity of light emanating from the scene is variable. Further complications are presented when the characteristic wavelength of light emanating from the light source varies for example, as the wavelength of a laser may vary with its operating temperature.
The present invention provides methods and apparatus for segmenting the reflected light of an illumination source, from the background clutter of a scene, thereby minimizing the effects of background clutter that can impede the utilization of structured lighting systems. Embodiments of the present invention are applicable to both static and dynamic scenes and provide cures to the issues and problems discussed above.